Reactors that are passive elements employing windings are used in various electric circuits and electronic circuits such as for the prevention of harmonic current in a power factor improvement circuit, the smoothing of current pulsation in a current source inverter and chopper control, and the step-up of direct current voltage in a converter. There are Patent Literature 1 to Patent Literature 4 as technical literature related to this type of reactor, for example.
Patent Literature 1 discloses a reactor including a coil, a core composed of a magnetic powder mixed resin that is packed inside and at the outer circumference of the coil, and a case that accommodates the coil and core, further including protrusions formed on an inner wall face of the case.
Patent Literature 2 discloses a reactor including: a pair of soft magnetic alloy pressurized powder cores of rod shape, each core being inserted into a thorough hole of a bobbin around which a coil is wound so that the core serves as an axis, around which the coil is wound and fixed; and a pair of plate-like soft ferrite cores connected with ends of the pair of soft magnetic alloy pressurized powder cores, respectively, to form a quadrangular composite core along with the pair of soft magnetic alloy pressurized powder cores. This reactor disclosed in Patent Literature 2 has an object of a size reduction and lowering loss, and a gap is provided at opposing portions of the soft magnet alloy pressurized powder core and the soft ferrite core so as to achieve an inductance of about 2 mH during OA.
However, in a case of such a gap being provided in a core member, problems in noise and magnetic flux leakage generally arise. In addition, the dimensional precision of the gap provided to the core member influences the inductance characteristic of the reactor; therefore, disadvantages also arise in that it is necessary to precisely form the gap, and manufacturing cost of the reactor increases. Employing a ceramic material may be included in the gap portion as noise control; however, there is a problem in that the manufacturing cost of the reactor increases also due to such noise control.
On the other hand, reactors employing air-core type coils are proposed in Patent Literature 3 and Patent Literature 4. Patent Literature 3 discloses an air-core reactor in which each coil turn is configured by overlapping a plurality of band-like unit conductors over each other. In this reactor, the thickness of coil turns in the radial direction of the reactor is less than the width in the axial direction thereof.
In addition, Patent Literature 4 discloses a reactor made by a plurality of disc windings wound around the circumference of an insulating cylinder and stacked in multiple steps in the winding axis direction, and each disc winding being connected to each other, in a state surrounded by a magnetic shielding iron core.